Creep characterization and damage assessment of long term service exposed P-22 grade of steel

This paper deals with damage assessment of 17 years service-exposed P-22 grade of steel used in main steam pipe of a boiler in a thermal power plant. Experimentally determined conventional creep data under identical testing condition were used in the present investigation. The value of λ (ratio of rupture strain to Monkman-Grant constant) infers that both service exposed as well as virgin material are ductile at 550 °C/145 MPa. It was observed that ductility in the service exposed material decreases with decrease in temperature at constant stress (145 MPa). It is also apparent that the values of strain fraction and life fraction are identical. A degree of scatter is observed in the Monkman-Grant constant (εs) value under identical test condition. Fractographic features and structure-property correlation study with optical, scanning and transmission electron microscopy were useful in predicting probable occurrence of experimental scatter.